thank you very much. This is meant to be a letter by which a professional "se compromete a participar" in a specific project, usually required to present the project for government funding. My attempt so far is: HEREBY I COMMIT MYSELF TO PARTICIPATE AS A (PROFESSION HERE)

By the way, Letter of intent I think is very close to what I'm looking for, according to wikipedia, "A letter of intent or LOI is a document outlining an agreement between two or more parties before the agreement is finalized."

I learned it as "engagement letter", working for many years at a Big Four accounting firm. It's used to define the legal relationship between a professional firm (e.g., law, investment banking, consulting, advisory or accountancy firm) and its client(s).